Traffic sensor strip

ABSTRACT

An elongated traffic sensor strip having a plurality of separate segments each appropriately spaced along the sensor to monitor traffic in separate lanes of a multi-lane roadway. A sealed envelope encloses segmented pressure-sensitive elements and a plurality of conductors connected to the individual elements. Metallic plates are positioned in the envelope along the length of the strip for attaching the strip to the surface of the roadway. In one embodiment, the elements have a pair of conductor plates normally held in spaced parallel relationship and movable to contact each other upon compression of the elements. In another embodiment, the elements have a coaxial cable which produces an electrical effect when subjected to pressure.

mem -ant: 35 l States Patent i 1 T, j

Mym

I mmc SENSOR mm I76 sw mp Richardll. Myers, 170a Woods,

15:} m. cl. t;08(; 1/00 {58} Field of Search 340/38 R; 177/136 T561 pReferences Cited UNITED STATES PATEN'IS 7 1.83655 12/193: Dunford s.340/38 R 7 2305.327 7/z939 Cooperr..- Mm 340/38 R 2.181318 1:939Greentrce .M 340/38R 292mm 1/:960 340/32 R FOREIGN PATENTS ORAPPLICATIONS 70,229 7/1952 ;Netherlands...l M... 340/38 R 1500120 9/[967France 340/38 R 1221 Bled:

1 Arlington, Tex. 76010 Nov. 7, 1973 an Ap'pl. M0,: 413.538 1 {521 US.Cl. 340/38 R; 174/113 A 2.004.271? "969 France m 340/38 R PrimaryExaminer-Thomas B. Habecker Attorney, Agent, or Firm-Richards, Harris 8:

. Medlock 71" ABSTRACT An elongated traffic sensor strip having aplurality of separate segments each appropriately spaced along thesensor to monitor traffic in separate lanes of a multi-lane roadway. Asealed envelope encloses segmerited pressure-sensitive elements and aplurality of conductors connected to the individual elements. Me-

tallic plates are positioned in the envelope along the;

length of the strip for attaching the strip to the surface of theroadway. In one embodiment, the elements have a pair of conductor platesnormally held in spaced parallel relationship and movable to contacteach other upon compression of the elements. In art'- other embodiment,the elements have a coaxial cable which produces an electrical effectwhen subjected to pressure.

10 Chin's, '12 Drawing Figures 1 v .QRMQ

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2 5% NM 4m 3 Sheet l0f2 us. Pat ent [0. 1,1915

p TRAFFIC'SENSORSI'RIP. BACKGROUND oFnramvENnoN.

The present invention relates. to traflic sensors for use in separatelyand simultaneously monitoring the traffic moving in a plurality ofdifferent lanes of a roadway In the design of roads, highways, bridges;and other structures and facilities',data oonceming trafiic speed anddensity; vehicle size,loading and type; and vehicle condition is used bytraffic engineers. The complexity of the data required for completeevaluation and planfeet of a coaxial cable as it is comprwed by avehicle ning of these structures at times requires the monitoring ofmany roadways simultaneously. including multi lane roadways. The volumeand complexity of the data matic traffic recorders have been devised forrecording data in a form which can ultimately be used with a computer inthe design of these structures.

necemary to make a complete evaluation renders man- Y ual trafficcounting impractical. Accordingly, auto- To provide the information forthese automatic traflic recorders, sensors are placed across theroadway. These sensors must be able to monitor traffic in multilaneroadways with complete lane isolation while sensing the variety of thedata required. In addition, the

sensors should have a low profile so that they are not rows;

FIG. 3 is a sectional view similar to H6. 2 illustrating an alternateembodiment of the present invention;

FIG. 4 is a graphical illustration of the tire patch contact as afunction of time; 7

FIG. 5 is a graphical illustration of the electrical efpassingthereover; y I

FIG. 6 is a graphical illustration of a differentiated output of acablei FlGS. 7 through 9 illustrate plan views of other embodiments of:n improved traflic sensor element of th present invention; and a FIGS.10 through 12 are sectional views of various I embodiments of thepresent invention.

oEscRn rroN or "me PREFERRED EMBODIMENTS Referring now to the Drawings,wherein like refer ence characters designate like or corresponding partsthroughout the several views, the tralfic analyzer sysreadily visible bythe motorists and have a gradual taporing profile to provide a smoothtire transition thereover. The sensors should be durable to resist wearand the possibility of damage from dirt or moisture. in addition, it isdesirable that the sensors be provided with means for anchoring in'theroadway so that they will remain in position over a prolonged period oftime.

Therefore, according to one embodiment of the prescnt invention, animproved trafiic sensor is provided having a pressure-sensitive elementenclosed in a sealed envelope. The envelope is formed between a pair ofpolyethylene sheets attached at their edges. The v element is segmentedalong its length corresponding to the number of lanes of the roadway. Aplurality of conductors are located in the envelope at the sides of theelement. A pair of metallic strips are sealed in the envelope on theoutsides ofthe-conductor to provide tabs for anchoring the sensor to theroadway.

It has also been discovered that when compressed, a

coaxial cable will produce an'electrical effect by generatinga iltagebetween the conductor and the-shield of g the cable. It is believed thatthe amplitude of the voltage is proportional to pressure on the cableand the frequency is a function of the speed and the tire patch lengthof the vehicle comprcsing the cable.

Therefore, according to another embodiment of the present invention, animproved sensor-is provided having a coaxial cable generating anelectrical effect upon compression thereof. i

r The objects and advantages of the present invention tern 10 with theimproved sensor of the present invention is illustrated in FlG.- l.Trafiic amlyaer system 10 is illustrated with a sensor strip 12positioned transversely across a rnultidane roadway l6. Roadway 16 isdivided into lanes 16a, 16b, 16c and 16d. Strip 12 is connected byshielded cable 20 to an electrical assembly 21 for recording theelectrical efi'ects generated by strip 12 as a vehicle passes over thestrip. Assembly 21 is sclficontained and can be located a safe distancefrom roadwayl6 out of view of the motorists. Assembly 2! is providedwith means for recording theelectrical effects generated by strip 12. IA control unit 22 may also be provided and selectively connected bycable 24 to initiate the operation of assembly 21 and provideidentifying inputs to assembly 21 as desired. Unit 22 can thenbedisconnected and y removed allowing assembly 21 to record the flow ofr trafiic information desired. Strip :2 has-individual sensor segments12a, 1%, 12

' and 12d spaced to correspond to lanes 16d, 16b, 16c

and 16:1. The individual segments are independently connected toassembly 21 to record vehicle data for each particular lane. In FIG. 2,the details of construction of one embodiment.of strip 12 areillustrated. in this embodiment.

segment l2a is illustrated enclosed in a sealed envelope v25 formed by apair of strips of polyethylene material 26 and 28. Strips 26 and 28extend the le'hgth of strip I I2 and are sealed at their edges 30 and32. Segment will be readily appreciated by those of ordinary skill in sthe art as the same becomes better understood by referf can: to thefollowing Detailed Description when coni a j sidered in connection withthe accompanying Drawings in which: I v f y r BRIEF onscnn nonor'meDRAWINGS- 7 FIG. 1 illustrates-a plan view of an improved trafiic" isensor element of the present invention shown sche-,

matically connected to a recorder in position on a four- 'lane roadwayrj, "1 J 12a is constructed from a commcrcialiy available resil ientenvelope 34 defining a chamber 36 in which are mounted a pair ofparallel spaced conducting plates 38 and 40. Plates 38 and 40 arenormally resiliently held in the position-illustrated in FIG. Zby a pairof cornpressible spacers 42 integrally moulded into the interior ofenvelope 34 to extend from the sides thereof.

Upon compression of envelope 34, plates 38 and 40 will contact. Suitableelectrical conductors are connected to plates 38 and 40 and areconnected through cable 2i!" to. amemhly 21. To assist in thecompression of envelope 34 an extending portion-$4 protrudes from l 1thulupper surface thereof.

Positioned on either side of segmcntlza six eon- E l 1 ductors 45 50.Conductors 45-50 can be appropriately 1 FIG. 2 is anenlarged sectionofthe device taken on line 2-2 of FIG. I, looking in the direction ofthe ar- 3 connected to the plates of segments I212, 12tand 12d.

J More or less conductors can be provided :srequired by the number oflanes in a given roadway to be monitored. y

A pair of plates 52 are bonded between strips 26 and through plates 52at spaced locations along the length of strip 12. l a

In addition to edges 30 and 32. an 1235 completely sealed at its ends. Aconnector may be provided in the 1 end of strip 12 adjacent to segment12a to attach cable l 28 adjacent to sealed edges 30 and 32. To anchorstrip I 12 to roadway l6, suitable fasteners 54 can be driven to theconductors for the pressure-sensitive elements of segments 12a, 12b,i2tand I211. Alternalively, cable 2.0 could be fixed to strip 12 and aconnector provided at assembly 2i. p

Assembly 21 is provided with means for sensing and recording contactbetween the plates of segments 12a,

12b. 12c and 12d, caused by the passage of an automobile thereover.

An alternate embodiment of the invention illus tratcd in FIG. 3. Thisalternate embodiment 58 is iden-.

tical to strip r2 illustrated in no- 2 except that a coaxhas been foundto P1} duce a distinct and identifiable signal upon passage of a vehiclethereover.

In the embodiment illustrated in FIG- 3, cable 60 is divided into aplurality of segments corresponding to the lanes to be monitored. Theseindividual segments are connected through conductors in cable 20 to unitThe operation of the coaxial cable when generating the electrical cheer'5 not completely understood. It is believed that the mirage in theconductor is created. ei-

ther through friction generated by shield element 66 i rubbing on theadiacent dielectric as cable 60 produces a static charge or by an effectsimilar to a piezoelectric 1 device caused by the molecular arrangementwhen the dielectric is extruded.

By using the cable as a variable current generator, recordingelectronics can be used with a low input impedance. These electronicscan be what is generally known as a charge amplifier, which partiallyintegrates the cable signal which is differentiated to some degree bythe cable. This output of this amplifier can be used insystems to mcauredynamic local road loading. in l addition, the output can be connectedto a threshold detector to produce signals from only these vehicleswhich exceed a desired road loading. This system minimizes the effectsof environmental factors such as temperature and moisture. 1

It may also be desirable to detect just the leading or trailing edge ofthe patch. This can be accomplished by differentiating the signalproduced by the cable. An example of the resultant signal from thisdifferentiation is illustrated in FIG. 6. The leading and trailing edgesof y I the patch produce sharp indications on the graph.

In FIG. 7, a third embodiment is illustrated using coaxial cable as atransducer providing lane segregation.

On this embodiment two closely spaced cables 80 and 82 are placed acm aroadway 84. in this illustration,

roadway 84 has trafiic lanes 84:: and 8412. Cable extends completelyacross lanes 84a and 84b while cable 82 extends only across lane 84a.

Cable 80 is connected to an AND gate 86 while cable 82 is connected togate 86 and amplifier 88'. The output l'of amplifier 88 will representthe traffic in lane 84a while the output of AND gate 86 will representthe traf- Zl-as previously described with respect to strip 12.

l 7 Cable 60 has central conductor 62 which is surrounded by dielectricinsulation 64. Shield element 66 surrounds insulation 63 and shieldelement 66 issurrounded by a second layer ofhigli wearresistant insula-7 tion 68.

In use. central conductor 62 shield element 66 l are connected to unit22 throdgh eahlelll. Ar! electri' cal effect in the form of voltage isgenerated betweenthe conductor and shield when avehicle passes overandc0mpressescable60. ln HO. 4, a time history of a tire patch presenceon the cable is graphically illustrated. At the tire first touches thesensor. During period A (from I to and therefore, the greatest change inforces on the cable occur. During the .B" (I: to 1 the force a on thecable is relatively constant and is approximately the maximumacceleration of the tire mbber occurs fic lane 84b. y I 7 By designingthe sensor in this manner the trafiic in more than two lanes can beseparated and recorded. in addition, the lanes can be segregated byplacing a small rigid tubular member around the cable in the lanes inwhich a signal is not desired. I I

7 in FIG. 8, another embodiment isillustrated using coaxial cable as alransfilcer providing lane segregation.

in this embodirnan lanes 84:: and 84!; have three cables 90, 91 and 92extending completely thereacross.

Cables 90 and 91 intersect at a point between the lanes. I I

Cables 91 and 92 are positioned transverse to the trai fie flow. Bydifferentiating the signal from the cables 1 l 90, 91 and 92 asdescribedabove. lane segregation and speed can be determined. Vehicles in lane84a would be indicated by signals in order from cables 99, .91 and 92.Vehicles in lane 84b would be indicated by signals in order from 9!,90and 92. In both instances the time proportional to the pressure in thetire and the acceler ation of the rubber away from the road at thesensor." 1

in the C" (1,10 :4). the tire is leaning the sensor with complexdynamics occuring in the tire.

in no. 5, a graphicillustrafion ofthe voltage gem ated in an 80-footlength of cable is shown as plot 70. The ordinate of the graph isvoltageand the abscissa is timcs'l'he amplitude A is believedto beproportional to vehicle speed and patch length; 1 g I the weight of thevehicle or exerted on theca--' ble. The period B is believed to beproportional to the lapse between cablesQl and 92 would be proportionalr l to speed. r j a In FIG. 9, anembodimentusing cables 94, 95and 96 isshown whichprevents coincidence at the cable cross 1 overofeables9439x195. ln thisembodiment, cable 94 I r l is protected by arigid metaltube 97 or the like to prea vent a coincident at the crossover point. Byusing the logic of the E6. 8. embodiment lane segregation and speed canbe determined.

H I In FIG. 10, anembodirnent for irstalling'a cable 100 i on a road bedmlisshovm. in this embodiment tempo- 7 my mounting of cable 100 isaccomplished by use of an adhesive tape 104. r

. in H6. 11, cable 100 is permanently attached by means of anadhesivecompound 106 which is shaped to cozcr cable 100 and adhere toroadway 102. A suitable adhesive compound 106 has been found to beMiracle Seal Mfg. by Revere Chemical Corp., 12407 Wootfiand Ave;Cleveland. Ohio 44120.

p In HG- 12, an additional embodiment is illustrated wherein the cable100 is inserted into a groove 108 in the roadbed 102. This grooveextends completely I across the lane to be monitored. A suitableadhesive compound 110 can be used to adhere the cable to the roadway.

7 Thus, it can be seen that the present invention prosicles a trafficsensor element which is portable and easy to install with laneisolatiomln addition, the profile of the sensor has a gradual buildupfor smooth transition making the sensor practically invisible to themowrists. The sensor is scaled to reduce the possibility of damage fromdirt and moisture, and flanges are provided to easily attach the sensorto the road.

In addition, the strip 58 can provide an inexpensive element whichfunctions even through the near lane is compressed. It is' believed thatby use of strip 58,

. speeds weights, patch lengths and axle counting can be accomplished.In addition, the strip 58 can be utilized to sense compression by otherthan the passage of vehicles thereover. V V

Hating thus described the invention, it is to be understood, of course,that the present invention may be practiced otherwise than as describedand thatnumerous modifications and alterations may be made thereinwithout departing from the spirit and scope of the ini vcntion as setforth in the appended claims.

in the claims: v I. A trafiic sensor which comprises:

' a. an elongated element which produces an electrical effect whencompressed;

b. a pair of insulating strips enveloping said element with faces ofsaid strips confronting; c. a plurality of parallel insulatedelectricalconduc- [tors positioned between said strips and alongsidesaid element, and v -d. a pair of rigid metallic strips bonded to saidinsulating strips at each edge thereof. 1 a 3 2.1he sensor of claim 1 inwhich said element comprises a pair of conductive plates normally spacedapart which make electrical contact when compressed.

3. The sensor of claim} wherein said clement comprises a coaxial cablehaving a central insulatedcondoctor, a shield around said insulator anda second in- 'sulator around said shield.

4. The sensor of claim 1 wherein said element is segmented along itslength.

- 5. A traffic sensor which comprises:

a. an elongated element which produces an electrical 7 effect whencompressed; v t b. an elongated insulating envelope housing said elementcentrally thereof;

c. a pair of rigid metallic strips of thickness substan i m tiaily lessthan the thickness of said element and bonded to the inner faces ofopposite sides of said insulating envelope, and

d. a plurality of insulatedelectrica] conductors positioned between saidstrips and extending parallel L t5 alongside said element.

6. The sensor of claim 5 inwhich said strips hav holes therethrough atspaced points along the length for receiving hold down anchors.

7. The sensor of claim. 6 wherein said element comprises a compressionfrictionresponsive coaxial cable having a central insulated conductonashield around i said insulator and asecond insulator around said shieldforming an elongated cylinder, bodies of filler material on oppositesides of said cable having sides which slope 25 from a thickness of saidcable to a thickness of said strips.

8. A traffic sensor which comprises:

a. an elongated compression-friction responsive co- 7 axial cable whichproduces an electrical effect 39 when compressed,

bl a wide thin insulating body enveloping and intimately adhered to saidcableforming a profile of gradual buildup for smooth transition of anauto- I mobile tire thereover, and i c. a pair of metallic membersbonded to said insulating body at opposite sides of said cable forsecuring said body to a roadway. 9. A trafiic sensor which comprises: I

40 axial cable having a central conductor, an insulator surrounding saidconductor, and a coaxial conductive shield clement intimately secured toand surrounding said insulator over its length wherein said cableproduces an electrical signal when com- V pressed, and

1 b. a wide thin insulating body enveloping and adhera ing said cable toa vehicle path and forming a profile of gradual buildup for smoothtransition of an I automobile tire 'thereover.

5n 10. The sensor of-claim 9- inwhich said body is ad- V hered to saidpath by adhesive material. g

fss

a. an elongated compression-friction responsive co-

1. A traffic sensor which comprises: a. an elongated element whichproduces an electrical effect when compressed; b. a pair of insulatingstrips enveloping said element with faces of said strips confronting; c.a plurality of parallel insulated electrical conductors positionedbetween said strips and alongside said element, and d. a pair of rigidmetallic strips bonded to said insulating strips at each edge thereof.2. The sensor of claim 1 in which said element comprises a pair ofconductive plates normally spaced apart which make electrical contactwhen compressed.
 3. The sensor of claim 1 wherein said element comprisesa coaxial cable having a central insulated conductor, a shield aroundsaid insulator and a second insulator around said shield.
 4. The sensorof claim 1 wherein said element is segmented along its length.
 5. Atraffic sensor which comprises: a. an elongated element which producesan electrical effect when compressed; b. an elongated insulatingenvelope housing said element centrally thereof; c. a pair of rigidmetallic strips of thickness substantially less than the thickness ofsaid element and bonded to the inner faces of opposite sides of saidinsulating envelope, and d. a plurality of insulated electricalconductors positioned between said strips and extending parallelalongside said element.
 6. The sensor of claim 5 in which said stripshave holes therethrough at spaced points along the length for receivinghold down anchors.
 7. The sensor of claim 6 wherein said elementcomprises a compression friction responsive coaxial cable having acentral insulated conductor, a shield around said insulator and a secondinsulator around said shield forming an elongated cylinder, bodies offiller material on opposite sides of said cable having sides which slopefrom a thickness of said cable to a thickness of said strips.
 8. Atraffic sensor which comprises: a. an elongated compression-frictionresponsive coaxial cable which produces an electrical effect whencompressed, b. a wide thin insulating body envoloping and intimatelyadhered to said cable forming a profile of gradual buildup for smoothtransition of an automobile tire thereover, and c. a pair of metallicmembers bonded to said insulating body at opposite sides of said cablefor securing said body to a roadway.
 9. A traffic sensor whichcomprises: a. an elongated compression-friction responsive coaxial cablehaving a central conductor, an insulator surrounding said conductor, anda coaxial conductive shield element intimately secured to andsurrounding said insulator over its length wherein said cable producesan electrical signal when compressed, and b. a wide thin insulating bodyenveloping and adhering said cable to a vehicle path and forming aprofile of gradual buildup for smooth transition of an automobile tirethereover.
 10. The sensor of claim 9 in which said body is adhered tosaid path by adhesive material.